Video and graphics display devices, such as television sets and monitors are known to sometimes provide faulty images. Some forms of faulty images include interference or shadowing, where a faint echo of the image is spaced a small distance from the intended image, or is distorted. Further faults include background noise, video ringing, incorrect control functionality, incorrect brightness, pincushion effects and refresh rate problems. Distortion is sometimes referred to as incorrect orthogonality, and is a measure of the geometrical accuracy of the image. Many displays use three color guns, red, green and blue, to generate multicolor images. The color guns must be properly aligned to provide sharp and accurate images. The images displayed on monitors and television sets are usually generated by a computer system in the case of monitors, or from an external broadcast source in the case of televisions. Monitors are also capable of displaying television signals that have been processed by a computer system. The sources of the broadcast signals range from ground based antennas and cable systems to satellite broadcast signals.
Many of the signals provided to television sets require significant processing and tuning prior to viewing on the television. Set top boxes for receiving, tuning and decrypting signals, as well as providing back channel communications to accounting and control facilities of the originator of the signals are common functions of such boxes. As can be seen, there is significant overhead in the equipment associated with the provision of the signal to either a monitor, television, or other type of display device. The complex processing of signals prior to the display device receiving the signal creates a problem with determining the source of a faulty image. Video drivers can be unique to each monitor, and they may also conflict with other software. Interference could be caused by a rain storm in the case of some small dish satellite systems, a nearby electronic device, overhead power lines, metal shelves, or operation of a motor attached to the same power supply system as used by the monitor or computer. It can be difficult to determine whether a faulty image is due to problems with the monitor itself, such as misaligned color guns, or is caused by interference, or problems with the received signal. It may also be caused by having the wrong video driver, or perhaps the video card in the computer is causing the faulty image.
Remote diagnosis by a repair person is virtually impossible, so in many cases, an expensive replacement display is needlessly sent to the user, wasting time, equipment and incurring high postage costs if the problem does not lie in the display. This creates a huge unnecessary burden on technical support services. If the repair person travelled to the display device, they would bring diagnostic equipment which would attach to the display and provide a test pattern as input to the display. The cost of sending a repair person is even more expensive than just shipping a new display. The test pattern comprised various geometric shapes and colors which allowed the repair person to visually inspect the displayed image for at least orthogonality, interference and correct alignment of the color guns. Such equipment is described in U.S. Pat. No. 5,345,263 to Miller. U.S. Pat. No. 5,247,358 to Richards shows the display of video signals stored on a computer for adjusting the brightness of the display. This again requires external equipment to determine the location of a faulty image.
Some display devices have microprocessors and on screen controls that provide menus for adjusting volume, channel and other characteristics of the display, including contrast and brightness. Viewing these menus can provide some clues as to where a faulty image may be originating, however, such menus are not designed for such diagnostic purposes, and do not provide good indications of problems. For instance, the images displayed in such menus usually use only one of the three color guns, and hence are incapable of showing improper alignment. The menu text is usually concentrated away from the edges of the displays, where orthogonality problems are most likely to be detected. A further display device is described in U.S. Pat. No. 4,901,147 to Tajima. The results of internal diagnostic routines are displayed by characters and graphics generated by the display circuitry and superposed on top of a video signal much like the display of on screen controls discussed above. Other monitors, such as a 100 inch monitor manufactured by Sony for military use are also thought to have some form of internal diagnostics.
There is a need for an independent diagnostic tool for displays which does not require additional equipment. There is also a need for a display diagnostic tool which is independent of the external display signals provided by computer systems, set top boxes and directly received from providers of such signals by the display device. There is a further need for a diagnostic tool which provides for ease of moving the display to a different location to determine if a local source of interference is causing the faulty picture. The tool must be simple to use in order for a non-technically oriented user to be able to diagnose problems with or without the aid of a telephone support person. It must also be inexpensive to implement.